Rotational state detecting apparatus
A rotational state detecting apparatus for detecting a rotational state of a direct current motor using a detection pulse outputted corresponding to rotation of the direct current motor includes a period measuring apparatus for measuring a period of the detection pulse, a period judging apparatus for judging whether the detection pulse is a rotation pulse indicating a rotational frequency of the direct current motor or a divided pulse into which the rotation pulse is divided on the basis of a period difference between a most recent rotation pulse and the detection pulse and a correcting apparatus for correcting the period of the detection pulse to a combined period of a plurality of serial divided pulses and generating the rotation pulse having the combined period in a situation where the detection pulse is judged to be the divided pulse.
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This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application 2005-316849, filed on Oct. 31, 2005, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTIONThis invention generally relates to a rotational state detecting apparatus. More specifically, this invention pertains to a rotational state detecting apparatus for detecting a rotational state of a direct current motor, in particular, a rotational frequency.
BACKGROUNDA direct current motor is an elemental motor driven on the basis of Fleming's left-hand rule. The motor is convenient because the motor generates torque in proportion to the level of current. In automobiles, the motor is utilized in a wide range of usage. For example, the motor is utilized as a starter motor, a mirror driving motor, a wiper driving motor, a power window driving motor, and a seat driving motor, or the like. For appropriately controlling a position and a velocity of each apparatus, a rotational state of the motor need to be accurately detected. Unlike a stepping motor, the direct current motor is not driven by driving pulses correspondent to a rotational frequency. Accordingly, for knowing the rotational frequency, a rotational state need to be detected by some methods.
There are various methods for detecting the rotational state. An encoder, in which a slit plate provided at a rotational shaft of the motor partially rotates in a photo interrupter, is one of the methods. To detect rotation of a rotational plate with magnetic poles with use of a magnetic sensor is another method. To detect rotational frequency from ripples of current flowing in the motor with use of characteristics of the direct current motor having a brush and an armature without using other sensors as described above, is still another method.
JP2003-9585A (Patent document 1) describes a rotational state detecting apparatus for detecting a rotational frequency of a direct current motor with use of ripple current flowing in the direct current motor as illustrated in
A method to detect a rotational frequency with use of ripple current of a direct current motor is simple and effective. Further, in a situation where the cutoff frequency of the filter is variable as described in Patent document 1, more accurate detection is available. However, in a situation where a brush in contact with an armature wears, high-frequency noise components of the ripple current tends to be large. Then, attenuating ability of the filter for the high-frequency noise becomes insufficient, and the high-frequency noise passes through the filter and is formed into pulses (refer to
A need thus exists for a rotational state detecting apparatus, in which influence from high-frequency noise can be restricted, and which can accurately detect a rotational state, in particular, a rotational frequency, of a direct current motor. The present invention has been made in view of the above circumstances and provides such a rotational state detecting apparatus.
SUMMARY OF THE INVENTIONAccording to an aspect of the present invention, a rotational state detecting apparatus for detecting a rotational state of a direct current motor using a detection pulse outputted corresponding to rotation of the direct current motor includes a period measuring means for measuring a period of the detection pulse, a period judging means for judging whether the detection pulse is a rotation pulse indicating a rotational frequency of the direct current motor or a divided pulse into which the rotation pulse is divided on the basis of a period difference between a most recent rotation pulse and the detection pulse and a correcting means for correcting the period of the detection pulse to a combined period of a plurality of serial divided pulses and generating the rotation pulse having the combined period in a situation where the detection pulse is judged to be the divided pulse.
BRIEF DESCRIPTION OF THE DRAWINGSThe foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein:
An embodiment of the present invention will be explained with reference to drawing figures.
As described above, there can be a situation where the detection pulse P receives influence from high-frequency noise and is divided as illustrated in
The period measuring means 1 measures a period of the input pulse (detection pulse) PI. The period judging means 2 judges whether the input pulse PI is the rotation pulse or the divided pulse, which is a division of the rotation pulse. Specifically, the period judging means 2 judges that the input pulse (detection pulse) PI is the divided pulse in a situation where the value of a period difference between a most recent rotation pulse and the measured input pulse (detection pulse) PI is larger than that of a reference period difference ΔT. In a situation where the input pulse (detection pulse) PI is judged to be the divided pulse, the correcting means 3 corrects the period of the detection pulse P to a combined period of plural serial divided pulses and generates the rotation pulse PO having the combined period.
As illustrated in a waveform chart of
The correcting means 3 integrates the divided pulses (period T3 and period T4) to recover the rotation pulse from the input pulses PI. Specifically, the correcting means 3 recovers the rotation pulse from the input pulses PI as follows in cooperation with the period judging means 2. The period judging means 2 calculates a period of a pulse integrated from the divided pulse period T3) and a following input pulse PI (summation can be performed by the correcting means 3 also). In an example illustrated in
In the meantime, the value of the reference period difference ΔT is set corresponding to the rotational frequency of the direct current motor. In other words, the value of the reference period difference ΔT is set corresponding to the period of the rotation pulse. In a situation where the period of the rotation pulse is short, the value of the reference period difference ΔT becomes small. In a situation where the period of the rotation pulse is long, the value of the reference period difference ΔT becomes large. In one embodiment, the value of the reference period difference ΔT can be set equal to or lower than approximately a half of the period of the rotation pulse.
In many cases, division of the input pulse PI is caused by high-frequency noise (ringing noise, harmonic noise, or the like) generated at the time of transient response such as rise or fall of pulses (refer to
As illustrated in
In the meantime, in one embodiment, the value of the reference period difference ΔT was set to a half of that of the period of the most recent rotation pulse. However, a ratio of the reference period difference ΔT to the period of the most recent rotation pulse can be appropriately set corresponding to a direct current motor in use. As a matter of course, the value of the reference period difference ΔT can be changed according to specifications and aging of the direct current motor. Further, the value of the reference period difference ΔT is not necessarily determined in terms of a ratio to the period of the most recent rotation pulse. The value of the reference period difference ΔT can be set by other methods, for example, by subtracting a certain value from the value of the period of the most recent rotation pulse.
As described above, the value of the reference period difference ΔT can be appropriately determined. The value of the reference period difference ΔT is set to a value larger than that of a period difference between the rotation pulses generated at the time of maximum acceleration or deceleration of the direct current motor. In a situation where the direct current motor accelerates or decelerates, some extent of difference is generated between the periods of serial rotation pulses. In a situation where the value of the reference period difference ΔT is set to a small value, there can be a possibility that the value of a period difference between the periods generated by acceleration or deceleration becomes larger than that of the reference period difference ΔT. In this situation, despite an absence of the divided pulse generation, erroneous detection of the divided pulse may occur. Accordingly, the value of the reference period difference ΔT is set to a value larger than that of the period difference between the rotation pulses generated at the time of maximum acceleration or deceleration of the direct current motor.
For example, at the time of acceleration/deceleration illustrated in
An example of the embodiment of the present invention will be explained with reference to FIGS. 5 to 7.
As illustrated in
As illustrated in
The period counter 12 resets a count value Tcur on the basis of the edge detection signal edge. After that, the period counter 12 increments the count value Tcur until next edge detection signal edge is inputted. As illustrated in
The adding portion 13 sums the count value Tcur with an offset value Tofst by an adder 31. An initial value of the offset value Tofst is zero. On the basis of a control signal sfrg from the control portion 15, and with use of a multiplexer 33, Tadd stored in a register 32 or zero is selected (refer to
The control portion 15 performs controls illustrated in a flowchart of
In a situation where the control portion 15 confirms that the edge detection signal edge is active (=High) (#1), the control portion 15 judges whether the value of a difference between Tref and Tadd is smaller than that of the reference period difference ΔT or not (#2). Because Tadd is a period of the input pulse PI, the difference between Tref and Tadd corresponds to a period difference between “the period of the most recent rotation pulse” and “the period of the measured input pulse PI (detection pulse)”. In a situation where the value of the period difference is smaller than that of the reference period difference ΔT, the measured input pulse PI is judged as the rotation pulse. In the meantime, in a timing chart of
In a situation where the input, pulse PI is judged not to be the divided pulse but to be the rotation pulse, values in registers 51, 52, and 54 are set as follows (#3). In the register 51, the control signal sfrg is set to Low. In a situation where next input pulse PI is evaluated, zero is selected as the value of Tofst in the adding portion 13. In the register 52, the period Tadd of the input pulse PI, which has been judged as the rotation pulse, is stored as the period Tref of the most recent rotation pulse. In other words, the value of the Tref is renewed for next judgment. In the register 54, a control signal rfrg is set to Low. The control signal rfrg is utilized in the pulse generating portion 14.
In the meantime, though it is not illustrated in
The pulse generating portion 14 generates and outputs the output pulse PO (detection pulse) on the basis of a period (Tpuls) of the rotation pulse. A register 42, in which Tpuls is stored, is renewed every time an edge of the input pulse PI is detected. In a situation where the control signal rfrg is Low, on the basis of the control signal rfrg and with use of a multiplexer 41, Tadd is selected and is stored in the register 42 as Tpuls. Tpuls is a value, which determines a period of the output pulse PO. A pulse generator 43 reads the value of Tpuls from the register 42, and memorizes the value of Tpuls as required basis. Then, the pulse generator 43 generates and outputs the output pulse PO, of which duration of High is a fixed value Thigh, and of which a period is Tpuls (refer to
Next, a situation where the input pulse PI is the divided pulse will be explained taking a situation where the periods of the input pulses PI is T3 and T4 in the timing chart of
Tref−Tadd=T2−T3>ΔT(≅T2/2)
From the calculation result described above, the input pulse PI is judged as the divided pulse. As illustrated in the timing chart of
In the register 51, the control signal sfrg is set to High. By this, at the time of evaluation of the next input pulse PI, Tadd (=T3) is selected as a value of Tofst in the adding portion 13. In the register 52, a value of Tref (=T2) is retained. It is because it is not judged that there is a new rotation pulse, and the value of the period Tref (=T2) of the most recent rotation pulse is not changed. In the meantime, similarly to Tree the value of the reference period difference ΔT is not recalculated either. Or, even in a situation where the value of the reference period difference ΔT is recalculated, because Tref is the same value, the value of the reference period difference ΔT is renewed to the same value. In the register 54, the control signal rfrg is set to High.
In a situation where the control signal rfrg is High, the value of previously renewed Tpuls (=the period T2 of the rotation pulse) is selected on the basis of the control signal rfrg and with use of the multiplexer 41 and is retained in the register 42. The pulse generating portion 14 continuous a process to generate and output the output pulse PO on the basis of the period Tpuls set at the time of detection of the previous edge. Accordingly, the output pulse PO of an original period T2 is generated and outputted without being influenced from the divided pulse.
Next, as illustrated in the timing chart of
Tofst+Tcur=T3+T4
The register 32 stores the summation result addout as Tadd on the basis of the edge detection signal edge. The value Tadd (=T3+T4) of the register 32 is outputted to the control portion 15 and the pulse generating portion 14. The control portion 15 calculates as follows and judges whether the summation Tadd of two periods can be a period of the recovered output pulse PO (detection pulse P) or not. In other words, the control portion 15 assumes that the input pulse PI has a period T3+T4, and judges whether the input pulse PI can be approved as the rotation pulse or not.
Tref−Tadd=T2−(T3+T4)<ΔT(≅T2/2)
From the calculation result described above, a virtual input pulse PI (summed period T3+T4) is judged as the rotation pulse. In the timing chart of
In a situation where the virtual input pulse PI (period T3+T4) is judged not to be the divided pulse but to be the rotation pulse, the values of the registers 51, 52, and 54 are set as follows (#3). In the register 51, the control signal sfrg is set to Low. By this, at the time of evaluation of the next input pulse PI, zero is selected as the value of Tofst in the adding portion 13. In the register 52, Tadd (=T3+T4, summed period), which has been approved as the period of the rotation pulse, is stored as the period Tref of the most recent rotation pulse. In other words, the value of Tref is renewed for next judgment. In the register 54, the control signal rfrg is set to Low.
In the meantime, the value of the reference period difference ΔT is also recalculated on the basis of the value of Tadd, which is the summed period. The recalculated result is stored in the register 53. For evaluation of the period of the next input pulse PI, the value of the reference period difference ΔT after renewal is utilized.
In the register 42 of the pulse generating portion 14, Tadd (=T3+T4) is stored as Tpuls on the basis of the edge detection signal edge. The pulse generator 43 generates and outputs the output pulse PO, of which the duration of High is the fixed value Thigh, and of which the period is Tpuls (=T3+T4) (refer to
As explained above, in the example, the adding portion 13 sums the periods of the serially measured plural divided pulses in cooperation with the control portion 15. The control portion 15 judges the summation of the periods of plural divided pulses as the period of the detection pulse P. The pulse generating portion 14 recovers the detection pulse P on the basis of the summed period. As described above, the edge detecting portion 11 and the period counter 12 mainly correspond to the period measuring means 1. The adding portion 13 corresponds to the period judging means 2 and the correcting means 3. The pulse generating portion 14 corresponds to the correcting means 3. The control portion 15 corresponds to the period judging means 2, the correcting means 3 and the reference period difference setting means 4 according to the embodiment of the present invention. Accordingly, according to the example described above, the rotational state detecting apparatus according to the embodiment of the present invention, including the period measuring means 1, the period judging means 2, and the correcting means 3, can be realized.
As explained above, according to the embodiment of the present invention, a rotational state detecting apparatus, in which influence from high-frequency noise can be restricted, and which can accurately detect a rotational state, in particular, a rotational frequency, of a direct current motor, can be provided.
According to an aspect of the present invention, a rotational state detecting apparatus for detecting a rotational state of a direct current motor using a detection pulse outputted corresponding to rotation of the direct current motor includes a period measuring means for measuring a period of the detection pulse, a period judging means for judging whether the detection pulse is a rotation pulse indicating a rotational frequency of the direct current motor or a divided pulse into which the rotation pulse is divided on the basis of a period difference between a most recent rotation pulse and the detection pulse and a correcting means for correcting the period of the detection pulse to a combined period of a plurality of serial divided pulses and generating the rotation pulse having the combined period in a situation where the detection pulse is judged to be the divided pulse.
In a situation where the detection pulse outputted corresponding to the rotation of the direct current motor receives high-frequency noise, or, in a situation where the detection pulse formed under influence of high-frequency noise is outputted, the rotation pulse, which indicates the rotation of the direct current motor, is divided. In other words, the rotation pulse is divided into a plurality of divided pulses, which has a period shorter than an actual period. Generally, periods of the serial rotation pulses do not have large difference therebetween in a situation where the rotation of the direct current motor is correctly indicated. Accordingly, as in the configuration described above, the detection pulse can be judged to be the rotation pulse or the divided pulse from the period difference between the most recent rotation pulse and the detection pulse. Because divided pulses are divisions of the rotation pulse, integration of the judged divided pulses enables to recover an original rotation pulse. According to the aspect of the present invention, there is no need of using powerful noise filters. Further, attenuation of signals caused by noise filters does not occur. Accordingly, the detection pulse, which accurately indicates the rotation of the direct current motor, can be obtained. Accordingly, a rotational state detecting apparatus, in which influence from high-frequency noise can be restricted, and which can accurately detect a rotational state, in particular, a rotational frequency, of a direct current motor, can be provided.
Here, furthermore, the detection pulse can be a ripple pulse obtained from a ripple current outputted from the direct current motor corresponding to the rotation of the direct current motor.
A method to detect the rotational frequency with use of ripple current flowing in the direct current motor is simple and effective. On the other hand, in a situation where a brush in contact with an armature wears, high-frequency noise of the ripple current tends to be large. In many cases, the high-frequency noise is harmonic components of a ripple frequency. Accordingly, the rotation pulse is divided at approximately a constant position (a position within the period) of the rotation pulse. In other words, the rotation pulse is divided into plural pulses without influence to the period of the rotation pulse. Accordingly, integration of the divided pulses can accurately recover the original rotation pulse. Generally, noise of ripple pulses increases corresponding to aging (wear of contacting portions such as a brush) of the direct current motor. However, the method, in which the divided pulses are integrated, can retain effect of correction without influence from aging. As described above, according to the aspect of the present invention, a rotational state detecting apparatus, in which a detection pulse can be obtained by a simple method, and in which influence from high-frequency noise can be restricted, and which can accurately detect a rotational frequency of the direct current motor, can be provided.
Furthermore, the period judging means can judge that the detection pulse is the divided pulse in a situation where the value of the period difference is larger than that of a reference period difference, and the value of the reference period difference can be set corresponding to a rotational frequency of the direct current motor.
The judgment whether the detection pulse is the divided pulse or not is made on the basis of the value of the period difference between the period of the divided pulse and the period of the most recent rotation pulse. Accordingly, in a situation where the reference period difference, which is a base of judgment, is a fixed value, there can be a situation where a relation between the value of the period of the rotation pulse, which differs corresponding to rotational speed, and that of the reference period difference largely fluctuates, which tends to cause lack of stability in judgment results. Here, in the aspect of the present invention, the value of the reference period difference is set corresponding to the rotational frequency (rotational speed) of the direct current motor. By doing so, fluctuation in the relation between the value of the period of the rotation pulse and that of the reference period difference can be small, and stability in the judgment results can be improved. Then, because the value of the reference period difference is sequentially renewed, the value of the reference period difference can preferably track changes of the rotational frequency of the direct current motor even in a situation where the rotational frequency of the direct current motor changes.
For example, the value of the reference period difference can be determined on the basis of that of the period of the most recent rotation pulse. The rotation of the direct current motor does not drastically change at the time of steady operation. Accordingly, there's not so large difference between the period of the most recent rotation pulse and the period of the detection pulse as the rotation pulse. Further, because the period of the rotation pulse indicates rotational speed of the direct current motor, the value of the reference period difference can be preferably determined by doing so. Further, for another example, the value of the reference period difference can be set to a half of that of the period of the most recent rotation pulse. In many cases, division of the detection pulse is caused by high-frequency noise (ringing noise, harmonic noise, or the like) generated at the time of transient response such as rise or fall of pulses. Because oscillations caused by the transient response converges logarithmically, magnitude (in this situation, amplitude) thereof becomes small in approximately a half cycle of the period to the extent that the oscillation does not influence in forming pulses. Accordingly, phenomena, in which the rotation pulse is divided into the divided pulses, occurs in a range of approximately half cycle of the period. Therefore, it can be assumed that the period of the divided pulse does not exceed approximately a half cycle of the period. In a situation where the value of the reference period difference is set to a half of that of the period of the most recent rotation pulse, calculation load can be light, stability in the judgment results can be good, and the reference period difference can preferably track the changes of the rotational frequency of the direct current motor.
Furthermore, the period judging means can judge that the detection pulse is the divided pulse in a situation where the value of the period difference is larger than that of a reference period difference, and the value of the reference period difference can be set to a value larger than that of a period difference between rotation pulses generated at the time of maximum acceleration/deceleration of the direct current motor.
In a situation where the direct current motor accelerates or decelerates, some extent of difference is generated between the periods of the serial rotation pulses. In a situation where the reference period difference is set to a small value, there can be a possibility that the value of difference between the periods generated by acceleration or deceleration becomes larger than that of the reference period difference. In this situation, despite an absence of the divided pulse generation, erroneous detection of the divided pulse occurs. As the aspect of the present invention, in a situation where the value of the reference period difference is set to a value larger than that of the difference between the periods of the rotation pulses generated at the time of maximum acceleration or deceleration of the direct current motor, such problems does not arise, and stable judgment results can be obtained.
The principles, preferred embodiment and mode of operation of the present invention, have been described in the foregoing specification. However, the invention that is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents that fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.
Claims
1. A rotational state detecting apparatus for detecting a rotational state of a direct current motor using a detection pulse outputted corresponding to rotation of the direct current motor, comprising:
- a period measuring means for measuring a period of the detection pulse;
- a period judging means for judging whether the detection pulse is a rotation pulse indicating a rotational frequency of the direct current motor or a divided pulse into which the rotation pulse is divided on the basis of a period difference between a most recent rotation pulse and the detection pulse; and
- a correcting means for correcting the period of the detection pulse to a combined period of a plurality of serial divided pulses and generating the rotation pulse having the combined period in a situation where the detection pulse is judged to be the divided pulse.
2. The rotational state detecting apparatus according to claim 1, wherein
- the detection pulse is a ripple pulse obtained from a ripple current outputted from the direct current motor corresponding to the rotation of the direct current motor.
3. The rotational state detecting apparatus according to claim 1, wherein
- the period judging means judges that the detection pulse is the divided pulse in a situation where the value of the period difference is larger than that of a reference period difference, and the value of the reference period difference is set corresponding to a rotational frequency of the direct current motor.
4. The rotational state detecting apparatus according to claim 1, wherein
- the period judging means judges that the detection pulse is the divided pulse in a situation where the value of the period difference is larger than that of a reference period difference, and the value of the reference period difference is set to a value larger than that of a period difference between rotation pulses generated at the time of maximum acceleration/deceleration of the direct current motor.
5. The rotational state detecting apparatus according to claim 2, wherein
- the period judging means judges that the detection pulse is the divided pulse in a situation where the value of the period difference is larger than that of a reference period difference, and the value of the reference period difference is set corresponding to a rotational frequency of the direct current motor.
6. The rotational state detecting apparatus according to claim 2, wherein
- the period judging means judges that the detection pulse is the divided pulse in a situation where the value of the period difference is larger than that of a reference period difference, and the value of the reference period difference is set to a value larger than that of a period difference between rotation pulses generated at the time of maximum acceleration/deceleration of the direct current motor.
Type: Application
Filed: Oct 30, 2006
Publication Date: May 17, 2007
Applicant:
Inventors: Muneaki Kurimoto (Obu-shi), Eiichiro Shigehara (Toyota-shi)
Application Number: 11/589,174
International Classification: G01B 7/30 (20060101);